Production of mattresses of the above type using liquid polyurethane in order to fasten the spring core to at least one opposite substrate area of polyurethane foam, in order to more rapidly produce such mattresses, is known in prior art from Danish Patent no. 146092 B.
From current production methods, it is known that this method can be employed by equipping one of the surfaces of the base piece with longitudinal streaks of liquid polyurethane, along the longitudinal edges of the base piece, onto which two longitudinal pieces of polyurethane foam are lowered and hardened. Thereafter, the area between the longitudinal pieces and the base piece is provided with the same substance onto which a spring core is lowered, as described in Danish Patent no. 146092 B. Finally, a top piece corresponding to the bottom piece is moulded in the same way, on top of the core and longitudinal pieces.
The result obtained is an unfinished mattress, lacking cross pieces in the short ends of the unfinished mattress. The cross pieces are manually thread into the openings between the bottom, top and longitudinal pieces and then glued to these edges with an adhesive. This task must be done very accurately, as the seams are especially subjected to strain during transport and use of the mattress. The manual process is consequently time consuming and expensive compared to an automated production line.
The glueing according to the present technique also has the disadvantage of seams consisting of two different materials, which will have a tendency to delaminate. The seams around the cross pieces therefore have the tendency to tear on such mattresses, even if the rest of the mattress is usable. Thus, this is a disadvantage for the user who must then send the mattress away for repair, or replace the mattress altogether, although it should not be necessary to do so given the condition of the other mattress parts.
There therefore exists a need for a process which makes it possible to produce mattresses of the above type in an automated manner, and wherein the seams of the pieces are of a strong and durable quality, and a quality that is as consistent as possible throughout the whole mattress.